1. Field of the Invention
The present invention relates to a manufacturing method of a substrate for liquid ejection head such as a substrate for ink jet recording head configured to implement recording by ejection of ink.
2. Description of the Related Art
Liquid ejection heads are used for a wide range of purposes such as printers, manufacturing apparatuses of display components and medical inhalers, and the application thereof to a lot of industries are expected in the future. Especially for a liquid ejection head for printers, an ink jet recording head is available, which can eject liquid droplets densely and precisely.
A substrate for such an ink jet recording head is conventionally manufactured by a semiconductor manufacturing technique using a substrate made of silicon. Specifically, the manufacturing begins with the formation, on a silicon substrate, of an ejection energy generating element including a heat generating resistant element and the like configured to generate bubbles of ink for ejection and a driving circuit to drive the heat generating resistant element by methods such as photolithography, vacuum film formation and etching. Then, an ink channel mold member to be a mold for an ink channel is formed on this substrate by photolithography, on which photosensitive resin is applied by spin coating for film formation. The thus obtained photosensitive resin layer is then exposed to ultraviolet rays, for example, to form an ink ejection port, and the ink channel mold member is removed, thus forming a nozzle layer (nozzle plate) made of this photosensitive resin and thus manufacturing a substrate for ink jet recording head.
Unfortunately, due to a difference in thickness of an underlayer under (on the substrate side) this photosensitive resin layer, e.g., due to a difference in thickness at a part of the ejection energy generating element on the substrate, the photosensitive resin to be the nozzle layer applied by spin coating on the ink channel mold member may have a non-uniform film thickness. The film thickness of the photosensitive resin layer directly relates to the thickness of an ink ejection port (orifice), and so is an important factor affecting the ejection performance.
As another problem caused by a difference in thickness of the underlayer such as at the ejection energy generating element, reflected light of the ultraviolet ray exposed to the photosensitive resin layer, which occurs due to such a difference in thickness, deforms a shape of the ejection port unlike a desired shape, thus adversely affecting the ink ejection performance of the ink jet recording head.
To avoid this, Japanese Patent Application Laid-Open No. H09-001809 (1997) proposes a method including an ink channel mold member formation step of disposing a dummy pattern made of the same material as that of the ink channel mold member at a region other than the ink channel as well, thus making the thicknesses of the ink channel mold member and a nozzle layer to be formed on this dummy pattern uniform. Japanese Patent Application Laid-Open No. 2009-178906 proposes a method of forming an anti-reflection film on a substrate having an ejection energy generating element thereon, whereby an ejection port is formed while suppressing reflection from the underlayer, and then removing this anti-reflection film.